pickup idea

i was thinking about a bass with 2 j pickups and one p.i know that has been done befor.i was thinking it be cool if you could have a a control that you can blend the two js togarther then have a pot to blend the j's and the p.

If they are passive pickups, the tone will suffer. The impedance changes dramatically as more pots and pickups are put into the circuit. You will be better off with an active preamp that handles 3 pickups. Check out the Fender Stu Hamm Urge-II model. It does what you are talking about.